Prior methods of machining the bearing spindle on a rockbit drilling arm were costly and required considerable machining skill to obtain satisfactory results. Machine operators using prior manufacturing methods had to account for five varibles, two angular and three linear, in positioning the rockbit arm forging. Because a given forging could be used to generate a variety of final configurations, elaborate fixtures have been used to adjust the positioning of the forging in accordance with the desired final configuration. Prior art fixtures, besides requiring a multiplicity of interchangeable spacer plate sets to accommodate various rockbit arm configurations, make use of shims to accomplish small adjustments. Shims are undesirable because, owing to the interrelationship between the aforementioned variables, a shim used to adjust one of the variables would affect the other dimensions which define the position of the rockbit arm prior to machining. Shim use in this type of machining is therefore associated with high part rejection rate and time consuming trial and error.